This invention relates generally to a cover plate of dielectric material which is converted to an xe2x80x9cactivexe2x80x9d cover plate by connecting it to a source of electric current through xe2x80x9clivexe2x80x9d terminals of a commercially available standard electrical device such as a common switch or wall receptacle, or combination thereof The term xe2x80x9cstandardxe2x80x9d refers to devices deemed standard by the National Electrical Code published by National Fire Protection Association, and as revised from time to time, and referred to in Guide to the 1975 National Electrical Code by Roland E. Palmquist, Publisher Howard W Sams, Indianapolis, Ind. (1975).
An xe2x80x9cactivexe2x80x9d cover plate is defined as one to which electrical power is directly supplied for use therein, that is, the plate consumes power. The active cover plate is fitted to an installed device without modifying or interfering with the existing wiring, and without being plugged into the device""s body. Each cover plate has embedded or sandwiched in it a xe2x80x9cloadxe2x80x9d and associated circuit components. More particularly, the invention relates to a cover plate in which the embedded load is an electroluminescent panel; by its electroluminescence the plate indicates that the device (whether switch or receptacle) is connected to a source of current, that is, energized. In another embodiment the invention relates to an active cover plate which is not electroluminescent, but supplies enough current to the xe2x80x9cloadxe2x80x9d which is integral with and xe2x80x9cslavedxe2x80x9d to the cover plate which itself functions, for example, as a radio transmitter or receiver; and, in yet another embodiment, an active cover plate is both electroluminescent and a transmitter or receiver, that is, the plate simultaneously provides enough power for the load which includes plural functional components.
Lighting devices which produce diffused light at relatively low intensity to provide sufficient visible light useful for human eyes to discern objects in the dark, are extensively used where low-level lighting is desirable. In particular, an electroluminescent cover plate is routinely used as a night-light over a conventional electrical receptacle, typically a duplex wall receptacle (using one of the two available plug-in portions or sockets) or over a receptacle which may include a light switch in a bathroom or bedroom (using the only available socket). A commercially available night-light, such as one sold under the trademark Limelite(copyright) by Austin Innovations as Model No. 11100, may be plugged into the socket of a conventional wall receptacle. The popularity of the electroluminescent cover plate derives from its inherently xe2x80x9cfail-safexe2x80x9d construction, and its ability to operate continuously for an arbitrarily long time, producing a subdued lighting.
In U.S. Pat. No. 3,588,489 to Gaines there is illustrated an electroluminescent panel between dual receptacles in a unique body case which houses three sets of opposed contact slots separated by a pair of vertically grooved transverse ribs. The panel is centered between openings for prongs to be plugged into the corresponding receptacle beneath the cover which is an application-specific cover plate for a wall-mounted duplex receptacle. The cover has a pair of opposed prongs which are inserted in opposed contact slots to provide current to the panel.
A few years later U.S. Pat. No. 3,307,030 to DeFrancisco disclosed an electroluminescent cover plate which provided plug apertures or a slot for a switch handle, but required that the plate have a pair of prongs which were to be plugged into a plug-in receptacle which required an extra central plug-in portion into which the prongs could be plugged into.
Very recently, in U.S. Pat. No. 5,485,356, Nguyen teaches a cover plate for a duplex receptacle, and to the rear surface of the plate is secured a resilient and flexible U-shaped conductive strip the arms of which provide contact plates which are inserted into contact members on each side of the body of the receptacle. The purpose of the device is to energize an indicator light when the receptacle is energized. The cover plate itself is not active and relies on the indicator light to indicate whether the receptacle is energized.
The cover plate may be active even on a switch, typically a wall-mounted light switch, which serves only to close or open the circuit for residential current, typically 110 V or 220 V, and which switch is grounded (for safety) through its frame to the metal box in which the switch is mounted.
It has been discovered that a pair of electrically conductive biasing means such as contacting spring-strips secured within a synthetic resinous (xe2x80x9cplasticxe2x80x9d) cover plate and in electrical contact with a load secured therein, provides adequate electrical contact to permit the use of the cover plate as an xe2x80x9cactivexe2x80x9d plate which simply and inexpensively accomplishes any one or more of several desirable functions. The circuit is secured to the cover plate in a manner so as to preclude human contact with a component of said circuit capable of inflicting an easily sensible and undesirable shock. Most preferably the circuit is embedded or sandwiched within the cover plate, transforming the cover plate into an xe2x80x9cactive devicexe2x80x9d.
Accordingly an active cover plate is provided for a standard electrical device having a unit-molded body on the exterior of which at least a pair of terminals is adapted for connection to a source of electrical current, without modifying the device""s body, and without interfering with the wiring of the device (whether switch or receptacle, or combination thereof) after it is installed. The circuit includes a xe2x80x9cloadxe2x80x9d supplied with enough power through contact with a pair of biasing contact means, each adapted to contact one of the terminals disposed exteriorly of the body of the electrical device. The contact resistance between the biasing means and the terminals is not important because the power requirement of the load is small.
In a specific embodiment, the load in an active cover plate is an electroluminescent material and the synthetic resinous material is preferably translucent or sufficiently transparent to visible light to allow illumination from the panel to be seen. When the cover plate is installed on a common and commercially available electrical device (switch or wall receptacle) the plate is illuminated continuously, while also indicating that the device is energized. Installation of the active cover plate does not require plugging the cover plate into the body of the device. The spring-strips, or equivalent contact means, contact the heads of screws on terminals supplying current on one or the other side of the body of the receptacle, or both sides; the screws are used to provide connection to available current supply leads. A wall receptacle has at least one plug-in socket opening forwardly thereof for receiving connecting prongs of a plug, to connect an electrical appliance or other device with a source of potential.
It has further been discovered that contacts such as spring-strips on the rear surface of an insulating cover plate for a standard device, provide good enough contact to transmit enough current to the electrodes of a luminescent panel, not only to generate luminescence in the cover plate but also to power any low voltage, low power (less than about 25 watts) electronic device small enough to be accommodated within the confines of a cover plate which is preferably not more than 10 mm thick; but the contacts do not provide enough power to present a danger to a human who comes in contact with the active cover plate. If desired the entire cover plate may be formed from an electroluminescent material, and electrodes for the material are connected to the opposed spring-strips.
Where the luminescence is not required, the active cover plate may be made from a conventional non-electroluminescent synthetic resinous insulating material. Such a cover plate itself functions as a radio transmitter activated by a microphone; or, as a radio receiver which picks up a signal either from the ambient surroundings or from AC lines conducting current for the household or building supply. The receiver actuates a miniature loudspeaker integral with the cover plate.
When a load requires more current than is typically required to activate an electroluminescent panel, that is more than about 0.1 watt, and the cover plate is to be used on a switch in a circuit for a residential application (light bulb, appliance, etc), to which switch only a power wire (black) and a ground wire (green) are connected, a circuit is provided which limits power to about 5 milliamps at the ground wire, the circuit comprising ratioed resistances and a rectifier, a load-limiting resistor and a battery means configured to deliver from 1 to 20 milliamps at a voltage in the range from about 5 to 15 volts.